Different proteins on immune cell surfaces or in the tumor microenvironment are targeted by currently approved ICIs, such as cytotoxic T-lymphocite-associate-4 protein (CTLA-4), programmed cell death protein 1 (PD-1) and its ligand (PD-L1), lymphocyte-activation gene 3 protein (LAG-3), and T cell immunoglobulin and ITIM domain (TIGIT), but many other ICIs are under development [4]. The gene discussed is PDCD1; the disease is neoplasm.